1. Field of the Invention
Contemporary computer systems are facing increasing difficulties with respect to thermal management. With the migration towards smaller processing geometry, higher clock speeds can be realized; at the same time, the transistor count of circuitry has grown exponentially. However, increasing clock speed and higher transistor counts translate into higher power consumption and, by extension, need for higher thermal dissipation.
In past years, performance-increasing design improvements have centered primarily on the central processing unit (CPU). As a side effect, also the thermal management efforts were primarily driven by the design and manufacture of CPUs. By comparison, other system components received relatively little attention. CPUs have one major drawback; they are extremely versatile but at the same time, because they have to handle so many different tasks, they perform relatively badly in specialized applications.
One case in point is the digestion of 3D graphics data. In short, any pixel output to the screen is essentially the product of 6 consecutive steps:
1. Application Tasks (the movement of objects according to tasks, movement of camera, aim of camera)
2. Scene Level Calculations (selection of detail level, object level culling, creating object mesh)
3. Transform
4. Lighting
5. Triangle Setup and Clipping
6. Rendering
Until the end of 1999, Application Tasks, Scene Level Calculations, Transform and Lighting were performed by the CPU, however, the performance levels achieved could not keep up with the demands of the software. Starting in 1999, simple video processors began to evolve into graphics processing units that initially took over the tasks of transform and lighting but soon evolved further into visual processing units. The terms graphics processing units (GPUs) and visual processing units (VPUs) are generalized, but both have in common that the integrated circuit used is capable of processing vertices and textures in more complex ways than merely operating with geometry data and texturing the resulting triangles.
On the contrary, modern GPUs/VPUs are capable of parallel execution of highly sophisticated programs called shaders that turn relatively simple geometry models into independent entities, or else assign color-changing routines to the individual triangles on a per pixel basis. It is understood that any of these geometry and pixel permutations require logic operations, and each logic operation requires clock cycles, and therefore, electrical energy. By extension, this implies that increasingly complex graphics require increasing amounts of electrical power to be dissipated as heat.
One particular obstacle in the management of thermal dissipation on the level of GPUs is the form factor definition of current computer systems. The currently prevailing ATX specifications have strict definitions of the space allotted for CPU cooling and they also define the distance between expansion slots on the motherboard. For low and midrange graphics cards, the available space suffices; however, as soon as one moves towards the high-end graphics sector, it is evident that a single slot cooling solution no longer suffices.
A short comparison of the power consumption of CPUs and GPUs shows that the power consumption of both groups has reached parity:
CPU Power Consumption Under Full Load*AMD Athlon64 (Venice - 2400 MHz)31W (Watts)AMD Athlon64 (San Diego - 2800 MHz)60WAMD Athlon64-X2 (Newcastle - 2000 MHz)48WAMD Athlon64-X2 (Toledo - 2600 MHz)81WIntel P4 670121WIntel P4 820D115WIntel P4 840 XE147WIntel P4 955 XE144W*http://www.lostcircuits.com/cpu/amd_fx60/6.shtml
Graphics Card Power Consumption Under Full Load**ATI RADEON X800 GT40 WATI RADEON X1600 GT42 WnVidia GeForce 6600 GT48 WnVidia GeForce 7800 GT57 WnVidia GeForce 7800 GTX80 WATI RADEON X1800 GT103 W nVidia GeForce 7800 GTX-51295 WATI RADEON X1900 XTX121 W **http://www.xbitlabs.com/articles/video/display/gpu-consumption2006.html\
Future graphics cards will have even higher power consumption, and expected values for the end of 2006 are around 180 W power consumption whereas it is expected that the power consumption of CPUs may stay at the present level or even decrease.
2. Description of Related Art
The increased power consumption of GPUs along with the restrictions of the available cooling space requires the consideration of alternative cooling is solutions. Of particular interest are solutions that actively move heat away from the source to a remote radiator that is not within the same thermal zone as the heat source. For example, currently used solutions use fans that blow hot air out of the case through ventilation slots in the mounting brackets using air pipes or tunnels. Other solutions use heatpipes. In advanced cases, water and thermoelectric cooling solutions are employed.
Even more important than the transport of heat out of the case or housing is the method of heat transfer between the heat source and the heat sink. Conventional heat transfer relies on transfer of heat from one surface to another using a thermal interface material (TIM). In general, this approach works, however, the actual removal of heat is limited by the thermal transfer rate of the heatsink, which is a matter of the thermal coefficient and the thickness of the material. Regardless of how advanced the design may be, this method of heat transfer relies on diffusion of heat through a solid body of material and is, therefore, slow.
A different approach uses fluids to transport the heat away from the source. Conventional waterblocks still rely on the same principle as that underlying air-cooling-based heatspreaders, that is, there is a passive heat diffusion from the IC to a thermal interface material and then to the heatspreader. In the latter, the heat still needs to diffuse from through a solid wall until it reaches waterchannels.
A different method of removing heat from a source is to bring the coolant into direct contact with the heat source, in this case the IC. In this regard, the laminar flow over the surface that needs to be cooled is the limiting factor for the heat transfer. There are different ways of optimizing the flow and the heat exchange, the most efficient method using a microcapillary system. A reasonable approximation of this approach can be achieved through the use of a micro-mesh that introduces turbulences in the flow as disclosed in U.S. patent application Ser. No. 11/314,433.
A problem with retrofitting a cooling system such as that described above is the inherent risk for spills and leaks. Spills can cause shorting of electrical contacts, likewise, leaks can cause overheating problems because of the resulting lack of fluid. Conventional mounting techniques use elastic O-rings but in a “mission-critical” application, this solution does not suffice. It is therefore understood that the implementation of a cooling solutions such as the one disclosed in U.S. patent application Ser. No. 11/314,433 requires mechanism that improves over those currently available.